摘要
利用曲靖VHF相干散射雷达2016年3月至2018年2月间持续观测数据,对电离层E区场向不规则体(field-aligned irregularities, FAI)回波形态特征进行统计分析,结果表明:E区FAI回波在地方时和高度上呈现出三个高发区间,日侧主要位于07:00—12:00LT和90~105 km,而夜侧两个高发区间分别对应于15:00—01:00LT和90~100 km以及18:00—04:00LT和100~115 km;E区FAI回波发生率还具有明显的季节变化,夏季5—8月是其高发期,而冬季的11和12月发生率为极小; E区FAI回波多普勒速度均在-85~85 m/s变化,而其谱宽主要分布在60 m/s以内,三个区间的平均多普勒速度均仅为数m/s,明显小于其平均谱宽,后者约在20~30 m/s.此外,高度分层研究发现,日侧E区FAI的各层平均多普勒速度总体上为负值,但在96 km高度上下薄层内存在一个小幅正值,而夜侧则以105 km高度为界,其上端各层均为负值,下端各层均为正值.曲靖E区FAI表现出典型的Ⅱ型回波特征,其生成和演变过程源自电离层电子密度梯度漂移不稳定性,子午风和低F区电场在其中起着重要作用.
Using the data of the VHF coherent scatter radar in Qujing from March 2016 to February 2018, the morphological characteristics of the ionospheric E-region field-aligned irregularities(FAI) echo are statistically analyzed. The results show that the E-region FAI echoes preferentially occur in three areas, the daytime echoes mainly appear during 07:00—12:00 LT at an altitude of 90—105 km, while the two nighttime echoes are clearly visible during 15:00—01:00 LT at an altitude of 90—100 km and during 18:00—04:00 LT at an altitude of 100—115 km, respectively. Moreover, E-region FAI echoes exhibit distinguishable seasonal variation, i.e., maximum occurrence during May to August, but the minimum occurrence in November and December. The Doppler velocity of these three echoes varies between-85 m/s and 85 m/s with a spectral width of 0—60 m/s, and the mean Doppler velocity is only several m/s which is much smaller than the mean spectral width(20—30 m/s).In addition,we find that the mean Doppler velocity of echoes in the daytime E-region is generally negative,but with a small positive value in the thin layer around the height of 96 km.However,the nighttime E-region is obviously separated by a height of105 km where the upper are negative,but the lower are positive.The characteristics of E-region FAI in Qujing is typical of type Ⅱ.The generation and evolution process are attributed to ionospheric electron density gradient drift instability in which the meridional wind and low F-region electric field play an important role.
引文
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